BMS 528 ch 22- DNA replication EXAM 2 (slide 30

BMS 528 ch 22- DNA replication EXAM 2 (slide 30)
Study online at https://quizlet.com/_gc77re

1. Model for helicase-mediated DNA unwinding: - Type II
catalyzes a
catalyzes the ATP-dependent unwinding of the
double stranded DNA to form stranded DNA break.

Two subunits alternate unwinding process upon
hydrolysis

The unwinding of DNA by helicase would cause the
double stranded DNA to become overwound if
there were no mechanism to relieve the torsional
stress
( )

2. Topoisomerase relieves torsional stress in DNA:

Steps:
1.) Topoiso-merase breaks DNA and binds to 5'
through a tyrosine. 3' remains (nick)

2.) 3' end rotates

3.) 3' OH attacks activated Phosphate the nick

3. Topoisomerase relieves torsional stress in DNA:

Topoisomerase I relieves this stress by one
strand of DNA by forming a covalent
phosphodiester bond to the 5'-phosphate

The 3' end is then free to to relieve the strain;
the torsionally relaxed DNA is religated and
unwinding by
can continue

4. Two types of topoisomerases I and II:

- Type I catalyzes a strand break.

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, BMS 528 ch 22- DNA replication EXAM 2 (slide 30)
Study online at https://quizlet.com/_gc77re
helicase single ATP
topoisomerase




phosphate open closing




nicking rotate helicase




single double




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